The cytokine interleukin-1 (IL-1) was initially described as a low molecular weight protein that acted in conjunction with plant lectins to stimulate the proliferation of murine thymocytes. The spectrum of IL-1-mediated biologic properties is diverse, and includes modulation of the cellular immune response as well as induction of acute inflammatory mediators, such as prostaglandins. Produced primarily by activated monocytes, macrophages and polymorphonuclear leukocytes, IL-1 exists as two distinct genetic forms, termed Interleukin-1.alpha. (IL-1.alpha.) and Interleukin-1.beta. (IL-1.beta.). Both IL-1.alpha. and IL-1.beta. are synthesized as precursor proteins of 31-33 kDa size and are subsequently cleaved to mature proteins of 15-17 kDa. The C-terminal halves of IL-1.alpha. and IL-1.beta. are often referred to as "mature" IL-1.beta. and "mature" IL-1.alpha.," respectively, while the N-terminal halves are referred to as the N-terminal IL-1.alpha. (or IL-1.beta.) propiece. The C-terminal halves of the precursor molecules of IL-1.beta. and IL-1.alpha. are not found within cells, suggesting that processing occurs concurrent with release. Notably, it is the C-terminal halves of the IL-1.alpha. and IL-1.beta. molecules that specifically interact with the Types I and II plasma membrane IL-1 receptors, and it is this interaction, prior to the current invention, to which all reported activities of IL-1 have been ascribed.
There are distinct differences between the IL-1.alpha. and IL-1.beta. molecules in terms of sequence homology, intracellular distribution, kinetics of synthesis and mechanisms of proteolytic processing to the mature, C-terminal forms. For example, the precursor form of IL-1.alpha. is processed between Phe 118 and Leu 119 by calpain, a calcium-dependent protease. The precursor form of IL-.beta. is processed by the specific IL-1.beta. converting enzyme (caspase) between Asp 116 and Ala 117.
Research has focused almost exclusively upon the activities of the processed C-terminal, membrane receptor-binding components of the IL-1 molecules. No specific biologic function has been ascribed to the 16 kDa N-terminal components of the precursors generated by proteolytic processing. Generation of polyclonal rabbit antibodies to synthetic peptides encoding epitopes for the N-terminal and C-terminal propieces of the IL-1.alpha. precursor molecule led to the histochemical observation that the N-terminal IL-1.alpha. propiece is present within the cell nucleus (Stevenson et al. (1992) J Cell Physiol 152:223-231). Subsequent studies using radioimmunoprecipitation of activated human monocyte lysates specifically recovered a 16 kDa protein with pI of 4.45, consistent with the predicted physicochemical properties of the IL-1.alpha. N-terminal propiece (Stevenson, et al. (1993) Proc Natl Acad Sci USA 90:7245-7249), thus demonstrating the existence of the native N-terminal IL-1.alpha. propiece within cells for the first time.
Examination of the cDNA sequence of the N-terminal IL-1.alpha. propiece revealed a polybasic region, T76-NGKVLKKRRL (SEQ ID NO:28), which had characteristics of a nuclear localization sequence (NLS) and could mediate nuclear localization of the propiece (Stevenson et al. (1997) Proc. Natl. Acad. Sci. USA 94:508-13). Introduction of the cDNA encoding the N-terminal IL-.alpha. propiece into cultured mesangial cells resulted in nuclear accumulation (Stevenson et al. id). Stable expression of the N-terminal IL-1 propiece results in apoptotic death of cultured mesanglial cells and immortalized Rat-1 fibroblasts, which was reported to suggest a role for the polypeptide in the removal of excessive cell populations during the resolution of glomerular inflammation (Turck et al. (1995) J. Am. Soc. Nephrol. 6:779, abstract no. 2052).
Apoptosis, or "programmed cell death," is the process by which a cell actively self-destructs in response to certain developmental or environmental stimuli. Apoptosis functions to control cell populations during embryogenesis, immune responses, hormone withdrawal from dependent tissues, normal tissue homeostasis, and tumor regression, as described in Duvall et al. (1986) Immunol. Today 7:115-119; Walker et al. (1988) Meth. Achiev. Exp. Pathol. 13:18-54; and Gerschenson et al. (1992) FASEB J. 6:2450-2455.
Apoptosis may be induced by immunologically mediated methods, such as antibody dependent cell cytotoxicity (K cell attack), viral infection, and attack by cytotoxic T lymphocyte effector cells, lymphotoxins, or natural killer (NK) cells. Further, apoptosis may be induced in tumor cells by a variety of physical, chemical, and biochemical agents, such as gamma radiation, UV light, heat shock, cold shock, cisplatin, etoposide, teniposides, DNA alkylating agents, macromolecular synthesis inhibitors, and the like. The apoptotic death process is associated with profound, well-defined morphological changes in the cell. Cohen et al., (1984) J. Immunol. 132, 38-42 (1984).
Current approaches to chemotherapy could benefit from selective induction of apoptosis in cancer cells. For example, while combination chemotherapy is often the treatment of choice, it often involves the use of ill-tolerated drugs and onerous side effects, which are largely associated with the non-specific nature of the therapy (Kruit et al. (1996) Br. J. Cancer 74(6):951). Thus, selective induction of apoptosis would be an attractive tool for cancer therapy. Unfortunately, development of apoptotic-based chemotherapy has met with many obstacles, include the identification of apoptosis-inducing agents that trigger cell death in cancerous cells, but do not substantially effect apoptosis in normal, non-cancerous cells. For recent reviews on the apoptosis in cancer chemotherapy see, e.g., Dixon et al. (1997) Ann. Pharmacother. 31:76-82; Guchelaar et al. (1997) Pharm. World Sci. 19:119-125; Mayer et al. (1997) Eur. J. Cancer Prev. 6:323-329; Tang et al. (1998) Prostate 32:284-293.
Thus, there is an urgent need for compositions and methods for use in chemotherapy that are both effective and selectively kill cancerous cells. The present invention addresses this problem.